Today, content discovery platform Outbrain is announcing it has secured $35 million in Series D funding in a round led by Index Ventures. Existing investors Carmel Ventures and Lightspeed Venture Partners also participated in the round. As a part of the deal, Dominique Vidal, partner at Index Ventures, will join the company’s Board of Directors.

The New York-based startup helps online publishers recommend additional content to their site’s readers through a website widget technology. The system combines contextual analysis, collaborative filtering (people who like X, also like Y) and personalization to determine which links to show readers at a given time. The personalization of the links shown is based on cookies, but is not tied to any personally identifiable information, nor is the data collected by one publisher shared with another.

You see Outbrain’s technology in action everywhere, but you probably don’t realize it. Its “recommended reading” widgets often show up at the bottom of a publisher’s page as sections titled “You might like:,” “We Recommend,” and “Elsewhere on the Web,” for example.

The service suggests two types of links to readers: inbound links to the publisher’s own content, which are not paid for, and outbound links to content on other sites which are paid for by Outbrain’s buyers, and involve a revenue share.

Outbrain’s recommendations are now viewed more than 3.5 billion times per month, generating over 200 million monthly clicks, the company reports. A growing number of those publishers are now using Outbrain’s newly launched mobile product, says Outbrain CEO Yaron Galai. Even though it’s only a few months old, mobile now accounts for 5%-10% of Outbrain’s business. With the Outbrain for Mobile widget, publishers can now add the same “recommended” sections to their mobile sites which link exclusively to other mobile-optimized content.

Video is another newer focus for the company, based on publisher demands. For publishers, explains Galai, “content is content” and they want one system to recommend it all. The video recommendation technology has been soft-launched and is live now on some partner websites. A public announcement will follow shortly.

Going forward, Outbrain wants to continue to expand to any platform where people are consuming content, says Galai, a statement which hints at the still untapped e-reader market.

As a result of this additional funding, which brings Outbrain’s total raise to $64 million, the company will focus on investing in both business development and global expansion. Outbrain had already been working towards these goals through its acquisition of Surphace from AOL (disclosure: TechCrunch is owned by AOL) and the opening of new offices in London, Paris and Hamburg. Going forward, there will be further moves into Europe as well as Asia.